Jet underreaming



March 3, 1964 w. B. BUCK i JET UNDERREAMING 3 Sheets-Sheet l Filed 061;. 2. 1961 FIG.

March 3, 1964 w. B. BUCK JET UNDERREAMING 5 Sheets-Sheet'l 2 Filed OC.. 2, 1961 MK m 2 3 Tw M 2 2 MB 0 V l ma r www

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March 3, 1964 w. B. BUCK 3,123,159

JET NDERREAMING INVENTOR. W. B. BUCK BY 7"? M77 A T TORNE K5 United States Patent O 3,123,59 .YET UNDERREANHNG n William E. Buck, @Mahoma City, Ghia., assigner to Phiilips Petroleum Company, a corporation of Belaware Filed Oct. 2, 1961, Ser. No. 142,161 16 Claims. (Cl. 175-67 This invention relates to a method and apparatus for drilling wells. In one aspect the invention relates to a method and apparatus for concurrent drilling and underreaming, the underreaming being eected by projecting jets of drilling liuid containing entrained drill cuttings against the wall of the borehole. In another aspect this invention relates to a method and apparatus for drilling with gaseous drilling uids, concurrently drilling and underreaming and periodically lowering a casing into the underreamed portion of the hole.

lt has been found that in certain types of formations and in certain areas it is highly advantageous to utilize a gaseous drilling uid rather than drilling mud. For example, in certain hard formations higher rate of peneration and reduced bit wear accompanying the use of a gaseous drilling fluid such as air or natural gas. However, in using a gaseous `drilling Huid a serious problem occurs when a water-bearing formation is encountered. Water entering the borehole wets the ne drill cuttings, thus causing these cuttings to tend to adhere to each other .and to the borehole walls, the bit and the drill string. This reduces the rate of drilling and, in severe cases, can cause a complete stoppage of the circulating ow.

lf ya casing string is run each time a water-bearing formation is encountered, in many instances several strings are required in drilling a relatively short length of borehole. This causes extra expense occasioned by the excessive amount of pipe in the well and the necessity for drilling with unusually large diameter bits during the beginning of the drilling operation. Alternatively the hole is reduced in diameter beyond a practical limit.

These ditiiculties can be avoided if ways can be found to lower a casing periodically as the well drilling operation continues and to form a seal between the casing and the well bore below each water-bearing formation as it is encountered and penetrated. This requires that the hole be underreamed prior to lowering the casing since the drill bit of necessity must be small enough to lower and raise through this pipe.

An object of my invention is to provide improved method and apparatus for concurrent drilling and underrearning.

Another object of my invention is to provide a method and apparatus for drilling wells with gaseous drilling fluid in areas wherein water-bearing formations are encountered.

Other aspects, objects and the advantages of my invention are apparent in the written description, the drawing and the claims.

According to my invention concurrent drilling and underreaming are accomplished by producing a pilot hole by physical contact of mechanical drilling means with a formation to be penetrated and simultaneously entraining drill cuttings in a stream of drilling fluid and directing the stream containing the cuttings against the wall of the borehole. Following the combined `drilling and underreaming operation to penetrate a water-bearing formation, a casing is lowered through this formation, a seal formed between the casing and the wall of the borehole below the formation, and the drilling operation continued.

I have provided improved well drilling apparatus cornprising means for drilling a pilot hole by physical contact with a formation to be penetrated and means for entraining drill cuttings in a stream of drilling fluid and for projecting the stream containing the cuttings against the wall of the borehole. According to my invention, means are provided for supplying drilling fluid to the drill string, for `discharging a portion of the drilling fluid to remove drill cuttings from the vicinity of the bit and means for discharging drilling iluid above the bit in a jet, entraining a portion of the drill cuttings in the jet and discharging them against the wall of the borehole to eifect the desired underreaming. A shell is provided surrounding the drill string providing a passageway yfor the drill cuttings, a ilow nozzle provided through the wall of the drill string cornnunicating with the fluid passageway therein, and an opening in the shell corresponding to each flow nozzle through which the jet is directed against the borehole. Means are provided for lowering a casing and for providing a seal between the casing `and the borehole wall.

In the drawing, FIGURE l is a schematic elevation, partly in cross section, illustrating the over-all operation according to my invention.

FlGURE 2 is an elevation, partly in cross section, of the lower portion of the borehole, the drill string and the combined `drilling and underreaming apparatus.

FIGURE 3 is a modification of the apparatus in FIG- URE 2 including guide vanes.

FiGURE 4 is another embodiment of my invention in which the shell is open at the top and bottom and in which venturis are used as the jet nozzles.

FlGURE 5 is another embodiment of my invention in which the shell comprises an inverted skirt.

FIGURE 6 illustrates the use of hard-surfaced ribs on the outside of the underreamer.

FIGURE 7 illustrates the use of a plurality of underreamers in which drill cuttings are used more than once on the way to the surface of the ground.

FIGURE 8 is an enlarged view of a portion of FIG- URE 3, partially broken away to reveal the guide vanes therein.

FIGURE 9 is an enlarged view of a portion of FIG- URE 5, partially broken away to reveal the guide vanes therein.

In the drawing a derrick 11 and draw works 12 are supported on a substructure 13. Derrick 11 is provided with a crown block 14 through which drilling line 15 is run to support traveling block 16. Traveling block 16 is provided with a hook 17 which in turn supports swivel 18 which includes bale 19. Supported in turn below swivel 1S are kelly 21, drill string 22 and drill bit 23. A source of drilling iluid under pressure, for example compressor 24, is provided and connected with swivel 1S by standpipe 25 and rotary hose 26. Rotary table 27 is provided to rotate kelly 2.1 and suspended drill string 22. Suitable driving means, not shown, are provided for rotary table 27 and draw works 12.

A conductor casing 23 is cemented in place as shown and supports a casing head 29, blowout preventers 31, ow nipple 32 and rotating head 33. A iiow line 34 is directed to a pit 35.

An inner casing 35 is provided with packer 37 and is supported in casinghead 29. Packer mud 38 is spotted above packer 37. Water-bearing formations are indicated at 39 and 39a Preferably packer 37 is a hook wall type so that the casing can be set a short distance above the bottom of the hole, approximately to l0 feet for example, This permits the underreaming operation to the started below the lower end of the casing, which reduces the possibility that there will be a small ledge immediately below the casing to prevent lowering it. However, if preferred, a suitable anchor packer can be used.

Underreaming apparatus 41 is provided in the drill string immediately above bit 23. This underreaming apparatus, as illustrated in more detail in FIGURE 2, comprises a shell 42, in the form of an inverted skirt, slightly smaller in diameter than bit 23, attached to driil string 22 at its upper end which is thereby closed. A ow nozzle 40 is threaded into the wall of the drill string as illustrated and thus provides communication with fluid conduit 43 inside drill string 22 and with the space outside drill pipe 22, in this embodiment discharging within shell 42. An opening 44 is provided in shell 42 in line with the discharge from flow nozzle 4i?. More than one flow nozzle 46 and corresponding openings 44 can be provided. Drill bit 23 is provided with the usual iiow passage 45 and is threaded to drill string 22 as shown. An orifice 46 is placed above bit 23. In some instances flow passages 45 are sized with respect to flow nozzle 4t) to provide the proper iiow distribution without orice 46. If desired, a suitable flow control valve, for example a spring loaded valve, to replace orifice 45 or a plurality of flow control valves, one for each ilow passage 45, can be used. In the operation of the invention as illustrated in FIGURES l and 2, after conductor pipe 2S is cemented in place and the equipment installed thereabove as shown, drilling normally is continued using a bit somewhat larger than inner casing 36 and the drilling proceeds in the usual manner, withdrawing the drill pipe to change the bit as necessary and circulating air from compressor 24 through standpipe 25, rotary hose 26, swivel i8, kelly 21 and drill string 22 to remove cuttings back to the surface of the ground and through flow line 34 to pit 35, until a water zone 39 is encountered. If necessary, chemicals or water can be added to assist in drilling during passage through this zone or, alternatively, mechanical means can be used to control the water while zone 39 is being drilled. After zone 39 has been penetrated completely and a suitable casing seat is encountered, drill string 22 is pulled from the hole and casing 36 lowered into place. An amount of packer mud is spotted just above the bottom of casing 36 in the annulus around this casing and packer 37 is set. Preferably, the packer is set some distance, for example 5 to l0 feet, above the bottom of the hole at this point. The drill string then is made up by picking up in order bit 23, underreaming apparatus 4l, drill string 22 and kelly 21. Drilling is continued, but now concurrent underreaming is accomplished. A portion of the drilling lluid circulates through ow passages 4S as before. However, orifice 46 maintains a substantial pressure drop through this area thus permitting a relatively high pressure to be maintained in fluid conduit 43 and thus a substantial portion of the drilling uid supplied at the surface of the ground is forced through flow nozzle 40. Cuttings removed from the formation by bit 23 are circulated through shell 42 to the vicinity of flow nozzle 4t) at which point these cuttings are entrained in the high velocity jet issuing through ow nozzle 40 and the jet with the entrained cuttings passes through opening 44 and impinges against the Wall of the borehole, thus eroding the wall causing an enlarging or underreaming action. Thus, the drilling is continued until a second water-bearing formation, such as formation 39a, is encountered. After this formation is drilled and a suitable casing seat reached, the drill string is withdrawn from the hole, casing string 36 manipulated to disengage packer 37 and then lowered into position with packer 37 below formation 4i). At this time a slug of packer mud is circulated down casing 35 and spotted just behind the bottom of this pipe, following which packer 37 again is set. Usually when a well is being drilled with a gaseous drilling uid, a supply of mud is kept at hand for emergency use. This mud can be used to circulate behind the packer mud to spot this mud in place following which the drill pipe is run and the mud remaining in the hole circulated out by the gaseous drilling fluid. The operation of drilling and concurrent underreaming followed by unseating of the packer 37 and lowering of the casing 36, respotting an amount of packer mud and reseating packer 37 can be repeated as often as necessary to seal off waterbearing formations as they are encountered.

In the embodiment of the underreaming apparatus illustrated in FIGURE 3 and FIGURE 8 guide vanes 47 are provided to direct the cuttings lifted from thebottom Y shell is a substantially cylindrical member 48. In this embodiment support vanes 49 hold the lower end of the shell in position around drill string 22 while the upper end is held in place by venturi flow nozzles 51 which extend through from fluid conduit 43 to the space outside shell 43. Each of these nozzles is provided with an entraining passage 52 which connects the annular space between drill string 22 and shell 43 with the throat of the venturi iiow nozzle. Thus, this annular space is connected with a locus of low pressure so that the drill cuttings which are lifted from the bottom of the well are readily entrained and discharged against the wall of the hole.

In the apparatus illustrated in FIGURE 5 and FIG- URE 9 the outer shell comprises an inverted skirt 53. Skirt 53 is attached to drill string 22 immediately above bit 23, thereby being closed at its lower end, the upper open end of skirt 53 helping to form a location of reduced upward velocity in the borehole. Drilling fluid discharging through bit 23 entrains the drill cuttings and lifts them upward in the hole. As the cuttings pass the upper edge of skirt 53 they enter the zone of reduced upward velocity of the drilling fluid (due to the enlarged annular area) and the lifting force is reduced so that the larger particles are allowed to drop into skirt 53 wherein they fall downward and are engaged by drilling duid 37 and then lowered into position with packer 37 below flowing through suitable flow nozzles and directed against the wall of the borehole.

In FIGURE 6 the outer shell 54 is provided with a plurality of ribs 55 which are surfaced with a hard, longwearing material, as for example silicon carbide, and thus this shell serves not only as the skirt of the underreaming apparatus but also serves as a stabilizer, the outer diameter of the shell including the ribs being substantially equal to the bit gauge.

In the embodiment of FIGURE 7 a plurality of shells 56, two or more, are spaced vertically above bit 23 thus serving to recirculate the drill cuttings and reuse them as they pass toward the surface of the ground, enlarging the borehole in steps.

A suitable packer mud can be made from the following ingredients:

200 bbls. water (fresh) 3500 lbs. bentonite 150 lbs. HV Driscose 50 lbs. caustic 600 lbs. SolteX lbs. Arcochrome 30G lbs. cottonseed hulls HV Driscose is a sodium carboxymethylcellulose additive and Soltex is a modified high molecular weight hydrocarbon, both available from Drilling Specialties Company.

Arcochrome comprises leather shavings and is available from Arnold & Clark Chemical Company.

The properties of this mud are:

Various combinations of the elements of the various modifications of the underreaming apparatus illustrated in FIGURES 2 through 7 are within the scope of my invention as well as modifications sncn as changes in dimension, shape, etc. Flow nozzles discharging within the shell such as illustrated in FlGURE 2 can be substituted for the venturi low nozzles Si in FIGURE 4 and a venturi nozzle on the other hand can be used with the skirt type shell of FIGURE 2 and FIGURE 3. Either type orr nozzle can be used in the embodiments of FIG- URE 5, FIGURE 6 and FGURE 7. Guide vanes 47 likewise can be utilized wherever necessary in any of the embodiments as can the ribs 55 illustrated in FGURE 6. In the embodiments illustrated, the outer shell of the underreaming apparatus is larger than that portion of the drill string 22 in that vicinity. In all instances, particularly where heavy drill collars are utilized at the lower portion of the drill string, a reduced diameter portion may be used in the immediate vicinity of the underreaming apparatus to leave room for the circulation of drill cuttings. If desired, the outer shell can be made substantially the same diameter as tne drill collars above.

In all of the embodiments most of the underreaming action is accomplished by the larger drill cuttings. In normal drilling practice there is some recirculation of drill cuttings in the immediate vicinity of the drill bit until such cuttings are reduced in size enough to reduce the weight-to-surface area ratio suiliciently that the particles are lifted by the ascending drilling iiuid. Where a light weight, low viscosity lluid is used, especially when the fluid is gaseous, the amount of circulation and regrinding of cuttings is increased. By the practice of my invention this recirculation is appreciably reduced. This is accomplished by the action of the underreaming operation by which the larger particles are caught up in the outwardly directed streams of drilling iluid and impinged upon the Wall of the borehole, thereby breaking up the larger particles. In some instances it is desirable to direct the llow nozzles at an angle upwardly in the hole to assist in the upward circulation of the entrained drill cuttings. This is particularly true in the use of multiple units as shown in FIGURE 7, although in all of the embodiments or my invention underreaming action is obtained when the llow nozzles are directed straight out at right angles to the drill string as well as when they are directed downward at a slight angle. Where insuhcient underreaming is obtained through the use of drill cuttings alone or when otherwise desirable, additional solid material can be supplied trom the surface of the ground to augment the underreaming action. Concurrent drilling and underreaming thus is obtained utilizing a combination of drill cuttings and solids supplied from the surface.

Reasonable variation and modication are possible within the scope of my invention which sets forth method and apparatus for concurrent drilling and underreaming by jet impingement of drill cuttings against the wall of the borehole and method and apparatus for drilling with gaseous drilling iuid by concurrent drilling and underreaming by jet impingement of drilling cuttings on the borehole wall and periodic lowering of a protective casing.

I claim:

l. A method for concurrent drilling and underreaming comprising the steps of producing a pilot hole by physical contact of mechanical drilling means with a formation to be penetrated, and simultaneously underreaming by entraining in a stream of drilling iluid cuttings produced by said physical contact and directing said stream containing said cuttings in a high velocity jet directly against the wall or" the borehole.

2. A method for concurrent drilling and underreaming comprising the steps of producing a pilot hole by contact of a drilling bit with a formation to be penetrated, circulating a drilling iluid through said bit to remove cuttings from the immediate Vicinity of said bit and lift said cuttings upward, discharging a stream of said drilling fluid above said drilling bit, entraining a portion of said cuttings in said stream and directing said stream and entrained cuttings in a high velocity jet directly against the wall of the borehole to effect underreaming.

3. Well drilling apparatus comprising means for drilling a pilot hole by physical contact with a formation to be penetrated, comprising a drill string and a drill bit, means to supply drilling iluid to said bit, means in said drill strinf7 above said bit for entraining in a stream of drilling fluid cuttings produced by said bit and for directing said stream containing said cuttings in a high velocity jet directly against the wall of the borehole, and means to direct said cuttings to said means for entraining.

4. Well drilling apparatus comprising means for drilling a pilot hole by physical contact with a formation to be penetrated, comprising a drill string and a drill bit, means' in said drill string above said bit for supplying a gaseous drilling fluid to said means for drilling, means for entraining in a stream of said drilling fluid cuttings produced by said bit and for directing said stream containing said cuttings in a high velocity jet directly against the wall of the borehole, and means to direct said cuttings to said means for entraining.

5. Well drilling apparatus comprising a drill string comprising a fluid conduit extending from the surface of the ground into a borehole, a bit attached to said drill string and communicating with said iluid conduit, means for supplying drilling fluid to said drill string, means for discharging drilling fluid to remove drill cuttings from the vicinity of said bit, means for discharging drilling nid above said bit and for entraining a portion of said drill cuttings and discharging said portion of entrained cuttings in a high velocity jet directly against the wall of the borehole to effect underreaming, and means to direct said outings to said means for discharging and entraining.

6. Well drilling apparatus comprising a drill string having a tluid conduit therethrough extending from the surface of the ground into a borehole, a bit attached to said drill string and communicating with said fluid conduit, means for supplying drilling iluid to said drill string, means for discharging drilling fluid to remove drill cuttings from the vicinity of said bit, and means for discharging driliing iluid above said bit and for entraining a portion of said drill cuttings and discharging said portion of entrained cuttings against the wall of the borehole to effect underreaming, comprising a shell surrounding said drill string above said bit providing a passageway for said drill cuttings, at least one llow nozzle through the wall of said drill string communicating with said iluid conduit and with the space outside of said drill string, and an opening in said shell corresponding to each said flow nozzle.

7. Well drilling apparatus comprising a drill string hc ving a lluid conduit therethrough extending from the surface of the ground into a borehole, a bit attached to said drill string and communicating with said lluid conduit, means for supplying drilling uid to said drill string, means for discharging drilling fluid to remove drill cuttings from the vicinity of said bit, and means for discharging drilling fluid above said bit and for entraining a portion of said drill cuttings and discharging said portion of entrained cuttings against the wall of the borehole to etlect underreaming, comprising a downwardly extending skirt surrounding said drill string above said bit, said skirt being attached to said drill string thereby eiecting closure of its upper end, and open at the bottom, at least one flow nozzle through the wall of said drill string communicating with said uid conduit to discharge within said skirt, and an opening in said skirt corresponding and aligned with each said iluid nozzle.

8. Well drilling apparatus comprising a drill string having a fluid conduit therethrough extending from the surface of the ground into a borehole, a bit attached to said drill string and communicating with said tluid conduit, means for supplying drilling iiuid to said drill string, means for discharging duid to remove drill cuttings from the vicinity of said bit, and means for discharging iluid above said bit and for entraining a portion of said drill cuttings and discharging said portion of said entrained cuttings against the wall of the borehole to eiect underrearning comprising a downwardly extending skirt surrounding said drill string above said bit, said skirt being attached to said drill string thereby eiecting closure of its upper end, and being open at the bottom, at least one flow nozzle through the wall of said drill string cornmunicating with said fluid conduit to discharge within said skirt, an opening in said skirt corresponding with and aligned with each said flow nozzle, and guides extending between said skirt and said drill stream to direct drill cuttings to the vicinity of each flow nozzle.

9. Well drilling apparatus comprising a drill string having a fluid conduit therethrough extending from the surface of the ground into a borehole, a bit attached to said drill string and communicating with said tluid conduit, means for supplying drilling fluid to said drill string, means for discharging fluid to remove drill cuttings from the vicinity of said bit, and means for discharging drilling fluid above said bit and for entraining a portion of said drill cutting and discharging said portion of said entrained cuttings against the wall of the borehole to effect underreaming, comprising a generally cylindrical shell open at top and bottom surrounding said drill string above said bit, at least one flow nozzle through the wall of said drill string and an opening in said shell corresponding to each said flow nozzle.

l0. Well drilling apparatus comprising a drill string having a fluid conduit therethrough extending from the surface of the ground into a borehole, a bit attached to said drill string and communicating with said uid conduit, means for supplying drilling iluid to said drill string, means for discharging drilling fluid to remove drill cuttings from the vicinity of said bit, and means for discharging drilling liuid above said bit and for entraining a portion of said drill cuttings and discharging said portion of said entrained cuttings against the wall of the borehole to eiect underreaming, comprising an upwardly extending skirt attached to said drill string to effect closure of said skirt at the bottom end, and being open at the top end, at least one flow nozzle through the wall of said drill string communicating with said fluid conduit to discharge within said skirt, and an opening in said skirt corresponding with and aligned with each said flow nozzle.

l1. Well drilling apparatus comprising a drill string having a fluid conduit therethrough extending from the surface of the ground into a borehole, a bit attached to said drill string and communicating with said fluid conduit, means for supplying drilling fluid to said drill string, means for discharging drilling lluid to remove drill cuttings from the vicinity of said bit, and means for discharging drilling liuid above said bit, and for entraining a portion of said drill cuttings and discharging said portion of entrained cuttings against the wall of the borehole to eiiect underreaming, comprising a shell surrounding the drill string above said bit providing a passageway for said drill cuttings, at least one flow nozzle through the wall of said drill string communicating with said fluid conduit and an opening in said shell corresponding to each said flow nozzle, and a plurality of hard faced ribs outside of said shell.

l2. Well drilling apparatus comprising a drill string having a iluid conduit therethrough extending from the surface of the ground into a borehole, a rotary bit attached to said drill string and communicating with said fluid conduit, means for supplying drilling iluid to said drill string, means for discharging drilling iluid to remove drill cuttings from the vicinity of said bit, and means for discharging drilling luid above said bit and for en-V training a portion of said drill cuttings and discharging said portion of entrained cuttings in a high velocity jet directly against the wall of the borehole to elect underrearning, including at least one venturi ow nozzle having an inlet, an outlet and a throat having a port communicating therewith, said inlet communicating with said tluid conduit, said throat communicating through said port with the space outside said drill string and said outlet directed toward the wall of the borehole.

13. Well drilling apparatus comprising a drill string having a liuid conduit therethrough extending from the surface of the ground into a borehole, a bit attached to said drill string and communicating with said iluid conduit, means for supplying drilling fluid to said drill string, means for discharging drilling iluid to remove drill cuttings from the vicinity of said bit, and means for discharging drilling luid above said bit and for entraining a portion of said drill cuttings and discharging said portion of entrained cuttings against the wall of the borehole, comprising a shell surrounding said drill string above said bit providing a passageway for the drill cuttings, at

least one ow nozzle through the wall of said drill string ycommunicating with said uid conduit and an opening in said shell corresponding to each said flow nozzle, and guides extending between said skirt and said drill string to direct drill cuttings to the vicinity of each said flow nozzle.

14. A method for drilling utilizing a gaseous drilling -iluid comprising the steps of producing a pilot hole by physical contact of mechanical drilling means with a formation to ybe penetrated, simultaneously underreaming by entraining a stream of drilling iluid cuttings produced by said physical contact and directing said stream containing said cuttings in a high velocity jib directly against the wall of the borehole, suspending the drilling operat1on, lowering a casing into the underreamed portion of the hole and continuing the drilling and underreaming operation.

l5. A method for drilling utilizing a gaseous drilling uid comprising the steps of producing a pilot hole by physical contact of mechanical drilling means with a formation to be penetrated, simultaneously underreaming by entraining in a stream of drilling iluid cuttings produced by said physical contact and directing said stream containing said cuttings against the wall of the borehole, suspending drilling and underrea-ming operations, lowering a casing into the underreamed hole, circulating and spotting a slug of casing mud adjacent the end of the casing and sealing the space between said casing and the wall of the borehole and continuing the drilling and underreaming operation.

16. Well drilling apparatus comprising a drill string having a fluid conduit therethrough extending from the surface of the ground into a borehole, a rotary bit attached to said drill string and communicating with said iluid conduit, means for supplying drilling i'luid to said drill string, means for discharging drilling duid to remove drill cuttings from the vicinity of said bit, and

10 means for discharging drilling uid above said bit and for References Cited in the le of this patent entraining a portion of said drill cuttings and discharging UNITED STATES PATENTS said portion of entrained cuttings in a high velocity jet directly against the Wall of the borehole to eiect under- 2307658 Appleby Ian' 5 1943 rearning, comprising a shell surrounding said drill string 5 2312018 Beckman u F613' 231 1943 above said bit providing a passageway for said drill 2'641444 Moon Jun@ 9 1953 Cuttings, at least one venturi ow nozzle having an inlet, 2720381 Quick Oct' 11 1955 1 2,946,565 Williams July 26, 1960 gehfiected toward the wall of tue borehole Outside 3,052,298 Malou Sept 4 1962 UNITED STATES PATENT OFFICE F CERTIFICATE OF CORRECTION Patent Nm 3,123,159 March 3, 1964 William B, Buck It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected belo Column 6, line 36, strike out "means for drillngr'?r..and

insert .instead bit line 38, strike out "bit" and insert instead meansk for drilling column 8*,I line 50, for "jib" read jet Signed and Isealed this 21st day of July 1964o (SEAL) Attest:

ESTON G. JOHNSON EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A METHOD FOR CONCURRENT DRILLING AND UNDERREAMING COMPRISING THE STEPS OF PRODUCING A PILOT HOLE BY PHYSICAL CONTACT OF MECHANICAL DRILLING MEANS WITH A FORMATION TO BE PENETRATED, AND SIMULTANEOUSLY UNDERREAMING BY ENTRAINING IN A STREAM OF DRILLING FLUID CUTTINGS PRODUCED BY SAID PHYSICAL CONTACT AND DIRECTING SAID STREAM CONTAINING SAID CUTTINGS IN A HIGH VELOCITY JET DIRECTLY AGAINST THE WALL OF THE BOREHOLE. 